Apparatus for use in treating upwardly-extending surfaces, including vertical surfaces, has in the past included apparatus which is constructed to be moved in a vertical direction up and down the surface. The particulate material in some cases is projected upwardly at an acute angle to the surface, as in the apparatus of U.S. Pat. No. 3,900,969; in other cases, the material is projected downwardly at an acute angle to the surface.
It is an object of the present invention to provide a machine which can be used to treat a vertical surface and attain a gravity-feed of rebounding material to a separating means of the apparatus whilst using a substantially horizontal direction impingement of the particulate material onto the surface.